The present invention relates to a needle printer of the type in which a plurality of printing needles are disposed in a conical housing. More accurately, such housing should be termed truncated because the tips of the needles project through the apex region in the front of the cone and in spaced-apart relation from each other.
The conical housing containing the printing needles establishes the printing head of the printer. Such printing heads are known and they include the base plate in the larger diameter rear portion of the cone which base plate carries the drivers for the needles. The needles must be held to some extent in the conical head and German printed patent application No. 1,249,570 discloses guide ducts for them. Lateral forces cause the needles to engage the duct walls in particular areas which establish a particular inflexibility in the guiding. In order to avoid unduly high friction, a relative large, overall play is needed but without compromising the accuracy of the guiding. Therefore, this particular guiding structure is rather complicated and expensive. Of course, one could use additional lateral forces in order to avoid an indefinite position of the printing needles but that would constitute an additional expenditure.
The German printed patent application No. 2,119,417 discloses a different kind of needle guiding system. In this case, each needle is held in a helical, metal wire coil. Unfortunately, it was found that in this particular kind of arrangement any shock and impact movement, i.e., rapid acceleration and deceleration of the needle produces lateral oscillations of the coils which are transmitted upon the needles and the tips will experience this lateral motion, at least to some extent, so that the particular printing pattern becomes distorted and blurred.